1. Field of the Invention
The present invention relates to a primer coating composition, an optical film including the same, and a polarizing plate including the same. More particularly, the present invention pertains to an optical film that includes a primer layer, such that transparency, optical property, mechanical strength, and attaching property to the polarizer are excellent, and the optical film may be usefully used as a polarizer protective film and the like. This application claims priority from Korean Patent Application No. 10-2009-0015875 filed on Feb. 25, 2009 in the Korean Intellectual Property Office (KIPO), the disclosure of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
Recently, display technologies using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD), an organic/inorganic EL display (ELD) and the like that are used instead of a known brown tube in accordance with the development of optical technologies are suggested and sold. In the above displays, use of various plastic films has been proposed, and more requirement properties have been highly developed. For example, in the case of liquid crystal displays, in order to be thinner and lightweight improve display property, various plastic films are used in a polarizing plate, a retardation film, a plastic substrate, a light guide plate and the like.
In the case of the polarizing plate, in general, it has a structure in which a triacetyl cellulose film (hereinafter, referred to as TAC film) as the protective film is layered on a polarizer by using an aqueous attaching agent composed of a polyvinyl alcohol aqueous solution. However, the polyvinyl alcohol film that is used as the polarizer and the TAC film that is used as the protective film for polarizer are not sufficient in terms of heat resistance and humidity resistance. Accordingly, if the polarizing plate including the films is used under a high temperature or high humidity atmosphere for a long time, since the degree of polarizing is lowered, the polarizer and the protective film are divided or an optical property is reduced, there are various limits in terms of the purpose. In addition, in the TAC film, the in-plane retardation (Rin) and the thickness retardation (Rth) are largely changed according to a change in the ambient temperature/humidity environment. If the polarizing plate that includes the TAC film as the protective film is applied to liquid crystal display devices, there is a problem in that the viewing angle property is changed according to the change in the ambient temperature/humidity environment, thus reducing the quality of image. In addition, since the TAC film has a high dimensional change ratio according to the change in the ambient temperature/humidity environment and a relatively large optical elasticity value, a change in retardation property locally occurs after evaluation of durability under the heat resistance and humidity resistance environment, thus easily reducing the quality of image.
In addition, in the case of when the polarizing plate is manufactured by using the TAC film as the polarizer protective film, an aqueous polyvinyl alcohol attaching agent is mainly used for adhesion to the polarizer including the polyvinyl alcohol component. At this time, in order to improve the adhesion strength, alkali treatment or corona treatment is performed on the surface of the TAC film. In the case of the known TAC film, since the hydrophilic group such as the hydroxy group is introduced to the surface of the film through the alkali treatment or the corona treatment, the adhesion strength may be ensured through hydrogen bonding to the polyvinyl alcohol attaching agent, but in the case of the acryl film, even though the corona treatment or the plasma treatment is performed, since the amount of the hydrophilic group that is introduced to the surface of the film is small, sufficient adhesion strength is not ensured.
As the material for compensating various disadvantages of the above TAC film, in the manufacturing of the polarizing plate, a cyclic olefin resin film or acryl film is proposed. However, even though the corona treatment or the plasma treatment is performed in respects to the cyclic olefin resin film or acryl film, since the amount of the hydrophilic group that is introduced to the surface of the film is small, the attaching property to the polyvinyl alcohol is low, such that there is a limit in practical application thereof.